125,246 research outputs found
Heat and mass transfer from the mantle: heat flow and He-isotope constraints
No full textTerrestrial heat flow density, q, is inversely correlated with the age, t, of tectono-magmatic activity in the Earth's
crust (Polyak and Smirnov, 1966; etc.). «Heat flow-age dependence» indicates unknown temporal heat sources in
the interior considered a priori as the mantle-derived diapirs. The validity of this hypothesis is demonstrated by
studying the helium isotope ratio, 3He/4He = R, in subsurface fluids. This study discovered the positive correlation
between the regionally averaged (background) estimations of R- and q-values (Polyak et al., 1979a). Such a correlation
manifests itself in both pan-regional scales (Norhtern Eurasia) and separate regions, e.g., Japan (Sano et al.,
1982), Eger Graben (Polyak et al., 1985) Eastern China rifts (Du, 1992), Southern Italy (Italiano et al., 2000), and
elsewhere. The R-q relation indicates a coupled heat and mass transfer from the mantle into the crust. From considerations
of heat-mass budget this transfer can be provided by the flux consisting of silicate matter rather than He
or other volatiles. This conclusion is confirmed by the correlation between 3He/ 4He and 87Sr/86Sr ratios in the products
of the volcanic and hydrothermal activity in Italy (Polyak et al., 1979b; Parello et al., 2000) and other places.
Migration of any substance through geotemperature field transports thermal energy accumulated within this substance,
i.e. represents heat and mass transfer. Therefore, only the coupled analysis of both material and energy
aspects of this transfer makes it possible to characterise the process adequately and to decipher an origin of terrestrial
heat flow observed in upper parts of the earth crust. An attempt of such kind is made in this paper.PublishedJCR Journalope
Fast Algorithms for Exact and Approximate Feasibility of Uncertain LMIs
No full textWe discuss fast randomized algorithms for determining an admissible solution for robust linear matrix inequalities (LMIs) of the form F(x, Δ)⩽0, where x is the optimization variable and Δ is the uncertainty, which belongs to a given set Δ. The proposed algorithm is based on uncertainty randomization: it finds a solution in a finite number of iterations with probability one, if a strong feasibility condition holds. Otherwise, it computes a candidate solution which minimizes the expected value of a suitably selected feasibility indicator function. The theory is illustrated by examples of application to uncertain linear inequalities and quadratic stability of interval matrice
Heat and mass transfer from the mantle: heat flow and He-isotope constraints
No full textTerrestrial heat flow density, q, is inversely correlated with the age, t, of tectono-magmatic activity in the Earth's crust (Polyak and Smirnov, 1966; etc.). «Heat flow-age dependence» indicates unknown temporal heat sources in the interior considered a priori as the mantle-derived diapirs. The validity of this hypothesis is demonstrated by studying the helium isotope ratio, 3He/4He = R, in subsurface fluids. This study discovered the positive correlation between the regionally averaged (background) estimations of R- and q-values (Polyak et al., 1979a). Such a correlation manifests itself in both pan-regional scales (Norhtern Eurasia) and separate regions, e.g., Japan (Sano et al., 1982), Eger Graben (Polyak et al., 1985) Eastern China rifts (Du, 1992), Southern Italy (Italiano et al., 2000), and elsewhere. The R-q relation indicates a coupled heat and mass transfer from the mantle into the crust. From considerations of heat-mass budget this transfer can be provided by the flux consisting of silicate matter rather than He or other volatiles. This conclusion is confirmed by the correlation between 3He/ 4He and 87Sr/86Sr ratios in the products of the volcanic and hydrothermal activity in Italy (Polyak et al., 1979b; Parello et al., 2000) and other places. Migration of any substance through geotemperature field transports thermal energy accumulated within this substance, i.e. represents heat and mass transfer. Therefore, only the coupled analysis of both material and energy aspects of this transfer makes it possible to characterise the process adequately and to decipher an origin of terrestrial heat flow observed in upper parts of the earth crust. An attempt of such kind is made in this paper
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
The 3He/4He Halo of the Kazbek Volcanic Center, Northern Caucasus
No full textManifestations of recent volcanism in the Greater
Caucasus are grouped in the El’brus and Kazbek volcanic
areas [1]. The last episodes of activity in the majority
of their eruptive centers date back to the Late
Holocene or even first centuries of the recent era
(El’brus Volcano) [2]. This implies potential volcanic
hazards in the Greater Caucasus. Therefore, it is important
to outline contours of this potentially hazardous
region with the maximal possible accuracy. The region
is characterized by indications of geodynamic stress,
such as recent eruptions, crustal deformations, seismic
activity, geothermal anomalies, and others. The 3He/4He value in natural gases can serve as one of such
indications.Published605–6083.2. Tettonica attivaJCR Journalreserve
On the convergence properties of the modified Polak--Ribiere--Polyak method with the standard Armijo line search
No full textZhang et al. [IMA J. Numer. Anal., 26 (2006) 629--640] proposed a modified Polak--Ribiere--Polyak method for non-convex optimization and proved its global convergence with some backtracking type line search. We further study its convergence properties. Under the standard Armijo line search condition, we show that the modified Polak--Ribiere--Polyak method has better global convergence property and locally -linear convergence rate for non-convex minimization. Some preliminary numerical results are also reported to show its efficiency.
References C. Li, A conjugate gradient type method for the nonnegative constraints optimization problems, J. Appl. Math., Volume 2013, Article ID 986317, 6 pages. D. Li and B. Tian, -step quadratic convergence of the mprp method with a restart strategy, J. Comput. Appl. Math., 235 (2011) 4978--4990. J. J. More, B. S. Garbow and K. H. Hillstrom, Testing unconstrained optimization software, ACM Trans. Math. Softw., 7 (1981) 17--41. E. Polak and G. Ribiere, Note sur la convergence de methodes de directions conjuguees, Rev. Fr. Inform. Rech. Oper., 16 (1969) 35--43. B. T. Polyak, The conjugate gradient method in extreme problems, USSR Comput. Math. Math. Phys., 9 (1969) 94--112. L. Zhang, W. Zhou and D. Li, A descent modified Polak--Ribiere--Polyak conjugate gradient method and its global convergence, IMA J. Numer. Anal., 26 (2006) 629--640. H. Zhu, Y. Xiao and S. Wu, Large sparse signal recovery by conjugate gradient algorithm based on smoothing technique, Comput. Math. Appl., 66 (2013) 24--32
Levitin-Polyak Well-Posedness in Vector Quasivariational Inequality Problems with Functional Constraints
No full text We introduce several types of Levtin-Polyak well-posedness for a vector quasivariational inequality with functional constraints. Necessary and/or sufficient conditions are derived for them.</p
Plio-Pleistocene sedimentary record from the Northwind Ridge: new insights into paleoclimatic evolution of the western Arctic Ocean for the last 5 Ma
No full textSediment core HLY0503-03JPC from the top of the Northwind Ridge provides the first confirmed Plio-Pleistocene record from the western Arctic Ocean, with calcareous microfossils uniquely preserved to ca. 5 Ma. Results are compared to nearby core P1-93AR-P23 from the ridge slope, which was previously used to reconstruct early Quaternary sea-ice conditions in the region (Polyak et al. in Quat Sci Rev 79:145–156, 2013), and is now re-dated to at least the late Pliocene. Ages were estimated primarily from strontium isotope stratigraphy on benthic foraminifers. Based on multiple physical, paleomagnetic, elemental geochemical, and paleobiological (foraminifers) proxies, we identify three major stratigraphic divisions (Units 1, 2a, and 2b) roughly representing upper to middle (“glacial”) Quaternary, lower Quaternary to Pliocene, and lower Pliocene to possibly upper Miocene (undated). Benthic foraminiferal assemblages were utilized to evaluate paleo-sea-ice conditions, while other proxies were used to interpret paleocirculation and sediment transport processes. Early Quaternary and older sediments indicate diminutive effect from glaciations, reduced sea-ice conditions, and a periodic strong current impact on the ridge top, possibly due to an enhanced Atlantic water flow. Ages derived from the first foraminiferal tests appearing at ca. 5 Ma likely indicate a redeposition pulse that we attribute to the onset of Pacific water throughflow via the Bering Strait. A large hiatus above this level in JPC3 spans most of the Pliocene. The Unit 2a/1 boundary, estimated to ca. 0.8 Ma, is marked by an abrupt faunal and sedimentary change, which is consistent with the major climatic shift that occurred during this time (Mid-Pleistocene Transition). Unit 1 exhibits a strong control from glacial cyclicity, with a progressive expansion of the Laurentide Ice Sheet primarily affecting the study region, and mostly perennial sea-ice conditions. Overall results suggest that the Pliocene and early Pleistocene may provide relevant paleoclimatic analogs for the rapidly changing Arctic environments of today
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